This used the same PCB as the GM853 “Bytewide” EPROM card, but had additional components added to support CMOS RAM ICs (note that the battery is missing in the above photo).

The sockets are arranged in 2 banks, A & B. Links are provided to allow the battery to back up either or both banks. The board was available in two versions: GM863-32 with 32k of RAM and GM863-64 with 64k of RAM.

SRAM was (is!) very useful as it allows memory contents to be retained even with power off. At the time of its release (1981), the HM6116 2Kx8 CMOS SRAM was about £30 each. By 1982 they had dropped to about £4 each in quantities of 10 upwards. Still, this card could take 16K of SRAM which was pretty useful. (I recently tried to get some low capacity CMOS SRAM chips – the smallest single chip I could get was 8Kx8 for £3.86 in one-off quantities. The cheapest was 128Kx8 for £2.11!)

I’ve cheated a little here. This photo was sent to me as being of a MP826 32k board (using 8 off HM6164 8k x8 chips). However it appears to be identical to the GM853 EPROM and GM863 RAM boards. I don’t know what went on – I’ll try to find out.

The manual I was supplied for the MP826 shows 16 off HM6116 2k x8 chips so something obviously changed somewhere as the pcb couldn’t accept that many. 🙂 Here’s the manual anyway:  MP826_Manual Unfortunately I don’t have manuals for either the GM853 or GM863.